Changed a stupid assert in request_pad.

Changed a stupid assert in request_pad.

Original commit message from CVS:
Changed a stupid assert in request_pad.
Some fixes for pullregion and EOS conditions.
Remove an unneeded check in the scheduler (check for NULL buffer)
some EOS fixes for pullregion in disksrc.
Removed the macro in the gstparse.h header 'cause it's internal to gstparse.c
Added a check in gstparse for NULL element.